Known in the art is a single-phase step motor (U.S. Pat. No. 3,370,189, 310-49, 1968) comprising three basic components: a coil with a core, a stator magnetic circuit with a hole and poles which are magnetically asymmetric, and a rotor unit composed of a rotor having a diametrically magnetized permanent magnet and a sleeve made of a non-magnetic material, having two bearings. The rotor unit is accomodated in the hole of the stator magnetic circuit. The non-magnetic sleeve with two bearings protects the rotor against dust. The known single-phase step motor has a magnetic circuit whose design is complex. The rotor is hard to be set with precision in relation to the stator or aligned with an external load mechanism. Such a motor is difficult to assemble.
The closest prototype is a single-phase step motor (British Pat. No. 1,459,981, H2A, 1976) whose design is simpler as contrasted to the one described above. The motor comprises a stator with a coil and a magnetic circuit having a core and a plate with a hole forming poles of the stator, which are magnetically asymmetric and connected by straps, as well as a rotor featuring a diametrically magnetized permanent magnet. The efficiency of this motor is not high because over 20 percent of the working flux of the rotor magnet closes through the straps between the stator poles, which results in reduction of the electromagnetic torque of the known motor. Moreover, no elements for accurate axial setting of the rotor in relation to the stator poles are provided in this motor. The same is true for rotor shaft alignment with respect to any external load mechanism. This makes the motor less reliable.